A terahertz ellipsometer, the basic preferred embodiment being a sequential system having a backward wave oscillator (BWO); a first rotatable polarizer that includes a wire grid (WGP1); a rotating polarizer that includes a wire grid (RWGP); a stage (STG) for supporting a sample (S); a rotating retarder (RRET) comprising first (RP), second (RM1), third (RM2) and fourth (RM3) elements; a second rotatable polarizer that includes a wire grid (WGP2); and a golay cell detector (DET).

Patent
   8736838
Priority
Feb 27 2009
Filed
May 21 2012
Issued
May 27 2014
Expiry
Aug 22 2029
Extension
60 days
Assg.orig
Entity
Small
9
52
currently ok
1. A terahertz ellipsometer or polarimeter system sequentially comprising:
a source (BWO) of terahertz electromagnetic radiation;
a first rotatable polarizer (WGP1);
a stage (STG) for supporting a sample (S);
a second rotatable polarizer (WGP2);
a detector (DET) of terahertz electromagnetic radiation;
said terahertz ellipsometer or polarimeter system further comprising a first element (RE1) and second element (RE2) between said source and detector of electromagnetic radiation, said first (RE1) and second (RE2) elements being capable of rotating continuously in use;
said terahertz ellipsometer or polarimeter system being characterized by said first element (RE1) and second element RE2 which are capable of rotating continuously in use being on the source, and detector of electromagnetic radiation sides of said stage (STG) and sample, respectively; and wherein said source and detector of electromagnetic radiation are a backward wave oscillator (BWO) and a golay cell (DET), respectively; and wherein said first (WGP1) and second (WGP2) rotatable polarizers each comprise a wire grid;
such that in use said backward wave oscillator (BWO) directs a beam (BI) of terahertz frequency electromagnetic radiation of a fundamental frequency to pass through said first rotatable polarizer comprising a wire grid (WGP1), then through said first element (RE1) which is capable of rotating continuously in use, then reflect from a sample (S) placed on said stage (STG) for supporting a sample, then pass through said second element (RE2) which is capable of rotating continuously in use, then pass through said second rotatable polarizer comprising a wire grid (WGP2), and, as output beam (BO) enter said golay cell detector (DET).
2. A terahertz ellipsometer or polarimeter system as in claim 1, in which the first (RE1) and second (RE2) elements which are capable of rotating continuously in use are each selected, from the group consisting of:
one thereof is a rotating polarizer comprising a wire grid (RWGP); and
the other thereof is a rotating retarder (RRET) comprising, in any functional order, first (RP), second (RM1), third (RM2) and fourth (RM3) reflective elements from each of which, in use, an electromagnetic beam reflects once, said first reflective element (RP) being prism (RP) which receives a beam through a first side thereof and exits a reflected beam through a third side thereof, said reflection being from a second side thereof oriented at prism forming angles to said first and third sides; said elements (RP) (RM1) (RM2) (RM3) being oriented with respect to one another such that the locus of the beam reflecting from the second side of said prism approaches said second reflective side thereof at an angle equal to or greater than that required to achieve total internal reflection within said prism (RP), and such that the locus of beam reflected from the fourth element in the sequence of elements is substantially colinear and without deviation or displacement from the locus of the beam received by the first element in said sequence of elements.
3. A terahertz ellipsometer or polarimeter as in claim 2 that further sequentially comprises:
a frequency multiplier (FM) following said backward wave oscillator (BWO);
a first concave parabolic mirror (PM1); and
a reflecting means (M1);
prior to said rotatable polarizer comprising a wire grid (WGP1);
and which further sequentially comprises after said polarizer comprising a wire grid (WGP1);
a second concave parabolic mirror (PM2);
prior to said a first rotating element (RE1) which is capable of rotating continuously in use;
there also further sequentially being, after said second element (RE2) which is capable of rotating continuously in use, a third concave parabolic mirror (PM3);
and there also further sequentially being, after said second rotatable polarizer comprising a wire grid (WGP2);
a fourth concave parabolic mirror (PM4) prior to said golay cell detector (DET);
such that in use said backward wave oscillator (BWO) directs a beam (BI) of terahertz frequency electromagnetic radiation of a fundamental frequency to said frequency multiplier (FM), from which frequency multiplier (FM) a beam comprising a desired frequency is caused to be reflected from said first concave parabolic mirror (PM1) as a substantially collimated beam, said substantially collimated beam then being directed to reflect from said reflecting means (M1) and pass through said first rotatable polarizer comprising a wire grid (WGP1) and reflect from said second concave (PM2) parabolic mirror through said first rotating element (RE1) which is capable of rotating continuously in use, then reflect from a sample (S) placed on said stage (STG) for supporting a sample, then pass through said second rotating element (RE2) which is capable of rotating continuously in use, reflect from said third parabolic mirror (PM3), pass through said second rotatable polarizer comprising a wire grid (WGP2), then reflect from said fourth concave parabolic mirror (PM4) and enter said golay cell detector (DET) as output beam (BO).
4. A terahertz ellipsometer or polarimeter as in claim 1 or 2 or 3 in which the first element (RE1) which is capable of rotating continuously in use is a rotating polarizer comprising a wire grid (RWGP); and the second element (RE2) which is capable of rotating continuously in use is a retarder (RRET) comprising, in any functional order, first (RP), second (RM1), third (RM2) and fourth (RM3) reflective elements wherein said first reflective element (RP) is a prism.
5. A terahertz ellipsometer or polarimeter as in claim 1 or 2 or 3 that further comprises at least one aperture (A) between said backward wave oscillator (BWO) and said golay cell detector (DET).
6. A terahertz ellipsometer or polarimeter as in claim 1 or 2 that further comprises, between said backward wave oscillator (BWO) and said golay cell detector (DET) at least one selection from the group consisting of:
at least one concave parabolic mirror (PM1) (PM2) (PM3) (PM4); and
at least one reflecting means (M1).
7. A terahertz ellipsometer or polarimeter as in claim 1 or 2 that further comprises a frequency multiplier (FM) following said backward wave oscillator (BWO).
8. A terahertz ellipsometer or polarimeter as in claim 1 or 2 or 3 that further comprises a chopper (CHP) between said backward wave oscillator (BWO) and said golay cell detector (DET).
9. A terahertz ellipsometer or polarimeter system as in claim 1 or 2 or 3 which further comprises means for rotating, as a unit, said:
stage (STG) for supporting a sample (S) and golay cell detector (DET) and any elements therebetween;
and/or as a unit said:
stage (STG) for supporting a sample (S) and backward wave oscillator (BWO) and any elements therebetween;
about a vertical axis centered at a midpoint of said stage (STG) for supporting a sample (S) such that the angle of incidence (0) at which said beam of terahertz frequency electromagnetic radiation approaching from said rotating polarizer comprising a wire grid (RWGP), and the angle of reflection (0) of said beam from said sample (S) placed on said stage (STG) for supporting a sample, can be adjusted.
10. A terahertz ellipsometer or polarimeter system as in claim 1 or 2 or 3, in which the stage (STG) for supporting a sample (S) is oriented to support a sample in a substantially vertical plane.
11. A terahertz ellipsometer or polarimeter system as in claim 1 or 2 or 3, in which the stage (STG) for supporting a sample is oriented to support a sample (S) in a substantially horizontal plane.
12. A terahertz ellipsometer or polarimeter system as in claim 2 or 3, in which the stage (STG) for supporting a sample is oriented to support a sample (S) in a substantially horizontal plane and in which the beam exiting said first element (RE1) which is capable of rotating continuously in use is directed thereto via left and right vertical sequences, each of first (FLS/FRS), second (SLS/SRS) and third (TLS/TRS) elements, such that the terahertz frequency electromagnetic beam exiting said first rotating element reflects from the first left side element (FLS) to the second left side element (SLS), then to the third right side element (TRS), from which it is directed to reflect from a sample (S) placed on the stage (STG) in a substantially horizontal plane toward the third left side element (TLS), which reflects said beam to the second right side element (SRS) toward said first right side element (FRS), from which said beam is directed into said second rotating element (RE2).
13. A terahertz ellipsometer or polarimeter system as in claim 2, in which a selected polarizer, which is capable of rotating continuously in use, comprises a wire grid is selected from the group consisting of:
a dual polarizing component system comprising non-Brewster Angle (NBR) and Brewster (BR) Angle components, wherein a beam of electromagnetic radiation that passes through said (NBR) reflects from additional reflective means (M1) and (M2), then from (BR), and continues as a polarized beam); and
a dual tipped wire grid polarizer system comprising first (WG1) and second (WG2) wire grid polarizers which have fast axes of polarization oriented with their fast axes parallel to one another, each thereof having first and second essentially parallel surfaces, such that essentially parallel sides of (WG1) are tipped with respect to the essentially parallel sides of (WG2), wherein a beam entering one of said first and second wire grid polarizers exits the second thereof in a polarized state, with unwanted reflections (R1) and (R2) being diverted away.
14. A terahertz ellipsometer or polarimeter system as in claim 1 or 2 or 3, in which the first and second elements which are capable of rotating continuously in use are rotated at relative speeds with respect to one another that form a ratio in the range of 1 to 10 or in the range of 10 to 1.

This Application is a CIP of Ser. No. 12/802,734 Filed Jun. 14, 2010, and of Ser. No. 12/802,638 Filed Jun. 11, 2010, and therevia is a CIP of Ser. No. 12/456,791 Filed Jun. 23, 2009, and via the foregoing Claims Benefit of Provisional Application Ser. No. 61/208,735 Filed Feb. 27, 2009, and further Claims Benefit of Provisional Application Ser. No. 61/281,905 Filed Nov. 22, 2009.

This invention which is subject in this application was developed in part under support provided by a Grant from the Army under Phase I ARMY STTR Contract No. W911NF-08-C-01121.

The portion of this invention concerning the “odd bounce image rotation system and method of use” in this application was developed in part under support provided by a Grant from the National Science Foundation under Phase II SBIR Contract No. 9901510.

The United States Government has certain rights in this invention.

The present invention relates to ellipsometer and polarimeter systems, and more particularly to an ellipsometer or polarimeter or the like system operating at THZ frequencies, and idealy comprising a backward wave oscilator; a frequency multiplier; a first concave parabolic mirror; a reflecting means; a first rotatable wire grid polarizer; a second concave parabolic mirror; a rotating wire grid polarizer; a stage for supporting a sample; a rotating retarder comprising first, second, third and fourth elements, a third concave parabolic mirror; a second rotatable wire grid polarizer; a fourth concave parabolic mirror; and a golay cell detector.

The practice of ellipsometry is well established as a non-destructive approach to determining characteristics of sample systems, and can be practiced in real time. The topic is well described in a number of publications, one such publication being a review paper by Collins, titled “Automatic Rotating Element Ellipsometers: Calibration, Operation and Real-Time Applications”, Rev. Sci. Instrum., 61(8) (1990).

Before proceeding, as it is relevant to the present invention, it is noted that ellipsometer systems generally comprise means for setting a linear or elliptical polarization state, (typically substantially linear).

Continuing, in general, modern practice of ellipsometry typically involves causing a spectroscopic beam of electromagnetic radiation, in a known state of polarization, to interact with a sample system at at least one angle of incidence with respect to a normal to a surface thereof, in a plane of incidence. (Note, a plane of incidence contains both a normal to a surface of an investigated sample system and the locus of said beam of electromagnetic radiation). Changes in the polarization state of said beam of electromagnetic radiation which occur as a result of said interaction with said sample system are indicative of the structure and composition of said sample system. The practice of ellipsometry further involves proposing a mathematical model of the ellipsometer system and the sample system investigated by use thereof, and experimental data is then obtained by application of the ellipsometer system. This is typically followed by application of a square error reducing mathematical regression to the end that parameters in the mathematical model which characterize the sample system are evaluated, such that the obtained experimental data, and values calculated by use of the mathematical model, are essentially the same.

A typical goal in ellipsometry is to obtain, for each wavelength in, and angle of incidence of said beam of electromagnetic radiation caused to interact with a sample system, sample system characterizing PSI and DELTA values, (where PSI is related to a change in a ratio of magnitudes of orthogonal components rp/rs in said beam of electromagnetic radiation, and wherein DELTA is related to a phase shift entered between said orthogonal components rp and rs), caused by interaction with said sample system. The governing equation is:
ρ=rp/rs=Tan(Ψ)exp(iΔ)

As alluded to, the practice of ellipsometry requires that a mathematical model be derived and provided for a sample system and for the ellipsometer system being applied. In that light it must be appreciated that an ellipsometer system which is applied to investigate a sample system is, generally, sequentially comprised of:

Various conventional ellipsometer configurations provide that a Polarizer, Analyzer and/or Compensator(s) can be rotated during data acquisition, and are describe variously as Rotating Polarizer (RPE), Rotating Analyzer (RAE) and Rotating Compensator (RCE) Ellipsometer Systems. It is noted, that nulling ellipsometers also exist in which elements therein are rotatable in use, rather than rotating. Generally, use of a nulling ellipsometer system involves imposing a substantially linear polarization state on a beam of electromagnetic radiation with a linear polarizer, causing the resulting polarized beam of electromagnetic radiation to interact with a sample system, and then adjusting an analyzer to an azimuthal azimuthal angle which effectively cancels out the beam of electromagnetic radiation which proceeds past the sample system. The azimuthal angle of the analyzer at which nulling occurs provides insight to properties of the sample system.

Continuing, in use, data sets can be obtained with an ellipsometer system configured with a sample system present, sequentially for cases where other sample systems are present, and where an ellipsometer system is configured in a straight-through configuration wherein a beam of electromagnetic radiation is caused to pass straight through the ellipsometer system without interacting with a sample system. Simultaneous mathematical regression utilizing multiple data sets can allow calibration of ellipsometers and evaluation of sample system characterizing PSI and DELTA values over a range of wavelengths. The obtaining of numerous data sets with an ellipsometer system configured with, for instance, a sequence of sample systems present and/or wherein a sequential plurality of polarization states are imposed on an electromagnetic beam caused to interact therewith, can allow system calibration of numerous ellipsometer system variables.

It is further noted that it was disclosed in a Co-Pending Parent Applications, Ser. Nos. 12/802,734 and 12/456,791 and 12/802,638, that the present invention is a practical ellipsometer or polarimeter system for application in the range of frequencies between 300 GHz or below. In that light it is to be understood that prior art demonstrates that it is not unknown to propose, or provide a system for, and practice of ellipsometry at Terahertz (THz) frequencies, however, a specific embodiment than makes such possible and which is suitable for general application in universities and industry etc., has not been previously disclosed. To the Applicant's knowledge, there are no commercially available THz ellipsometers or polarimeters available in the market place.

While Synchrotrons have been used to provide THz frequency band electromagnetic radiation in ellipsometers, it is not remotely possible to provide a Synchrotron at every location whereat it is desired to practice THz ellipsometry. The present invention provides combination of many elements, which results in a novel, practical system for general application in the market place.

Before proceeding, it is of benefit to define some terminology. First, a generally accepted range for what constitutes a Terahertz range of frequencies is from 3×1011 (ie. 300 GHz), to 1.3×1012 (ie. 1.3 Thz), Hertz. The Terahertz range is sandwiched between the microwave, (the high end of which has a wavelength of 1 millimeter), and the far-infrared, (the long-wavelength edge of which is 100 micrometers), ranges of wavelengths/frequencies.

Next, it is noted that a number of sources of Terahertz (THz) electromagnetic radiation exit. For instance, a Smith-Purcell cell is a device which directs an energetic beam of electrons very close to a ruled surface of a diffraction grating. The effect on the trajectory of the beam is negligible, but a result is that Cherenkov radiation in the Terahertz frequency range can be created, where the phase velocity of the electromagnetic radiation is altered by the periodic grating. Another source of Terahertz radiation is a Free Electron Laser. In this source a beam of electrons is accelerated to relativistic speed and caused to pass through a periodic transverse magnetic field. The array of magnets is sometimes called an undulator or “wiggler” as it causes the electrons to form a sinusoidal path. The acceleration of he electrons causes release of photons, which is “synchrotron radiation”. Further, the electron motion is in phase with the field of said released electromagnetic radiation, and therefore the fields add coherently. Instabilities in the electron beam resulting from interactions of the oscillations in the undulators lead to emission of electromagnetic radiation, wherein electrons radiate independently. The wavelength of the emitted electromagnetic radiation from the electrons can be adjusted by adjusting the energy of the electron beam and/or magnetic field strength of the undulators, to be in the Terahertz range. Another source, (and preferred in the present invention), of Terahertz frequencies is a Backward Wave Oscillator (BWO), which is a vacuum tube system comprising an electron gun that generates an electron beam and causes it to interact with an electromagnetic wave traveling in a direction opposite to that of ejected electrons such that THz frequency oscillations are sustained by interaction between the propagating traveling wave backwards against the electron beam.

It is also disclosed that numerous detectors exist for monitoring Terahertz range electromagnetic radiation. One example is a Golay cell which operates by converting a temperature change resulting from electromagnetic radiation impinging onto material, into a measurable signal. Generally, when electromagnetic radiation is caused to impinge on a blackened material it heats a gas, (eg. Xenon) in an first chamber of an enclosure, and that causes a distortable reflecting diaphram/film adjacent to said first chamber to change shape. In a second chamber, separated from the first by said diaphram/film an electromagnetic beam is caused to reflect from the film and into a photocell, which in turn converts the received electromagnetic radiation into an electrical signal. A Bolometer is another detector of monitoring Terahertz range electromagnetic radiation, but operates by using the effect of a changing electric resistance caused by electromagnetic radiation impinging onto a blackened metal.

It is also noted that there are Solid State sources and detectors of Terahertz frequency electromagnetic radiation. For instance, an identified reference by Nagashima et al. discloses that THz pulses can be generated by a bow-tie photoconductive radiation antenna excited by a mode-locked Ti-saphire laser with 80 Fs time width pulses, and a detection antenna can be formed from a dipole-type photoconductive antenna with a 5 micron gap fabricated on thin film LT-GaAs. Further, it is known that a company named AB Millimeter in Paris France, supplies a system that covers the entire range from 8 GHz to 1000 GHz with solid state source and detector devices.

Before disclosing known references, it is noted that computer searching at the PTO Website for Patents and Published Applications containing the words:

Further, a PTO Website Search for Patents and Published Applications containing the words:

A Patent to Wang et al., U.S. Pat. No. 5,914,492 is of interest as it describes free electron lasers used in combination with a Golay cell and Smith-Purcell detectors. However, it does not describe application in ellipsometry or polarimetry.

A Published Application, US2006/0050269 by Brownell describes use of a free electron laser and a Smith-Purcell detector, but not in the context of ellipsometry or polarimetry.

An article titled “Gain of a Smith-Purcell Free Electron Laser”, Andrews et al., Phy. Rev., Vol 7, 070701 (2004), describes use of Smith-Purcell Free Electron Laser.

U.S. Pat. No. 2,985,790 to Kompfner is disclosed as it describes a Backward Wave Oscillator.

U.S. Pat. No. 2,880,355 to Epsztein is disclosed as it describes a Backward Wave Oscillator.

Known References which describe Ellipsometers which operate in the THz frequency range are:

A Patent to Herzinger et al. U.S. Pat. No. 6,795,184, describes an “Odd-Bounce” system for rotating a polarization state in an electromagnetic beam. Patents disclosed in the Application leading to U.S. Pat. No. 6,795,184 are:

An additional relevant Patent is U.S. Pat. No. 6,268,917 to Johs. This Patent describes a combined polychromatic electromagnetic radiation beam source comprising beam combiners.

It is also disclosed that the J.A. Wooliman Co., Inc. has marketed an IR range Ellipsometer, called the IR-VASE®, for many years. Said instrument provides capability from 10 THz to 150 THz and is a Variable Angle, Rotating Compensator system utilizing a Bomen FTIR Spectrometer. Further, it comprises an FTIR Source, and an Odd-Bounce image rotating system for rotating a polarization state imposed by a wire-grid polarizer. It is noted that as marketed, this system has never provided the capability to reach down to 1 THz, which capability was achieved via research in developing the present invention.

Additional references which describe ellipsometry practiced in the THz range are:

Additional references which describe sources of Terahertz frequency range electromagnetism are:

It is noted that the Search Report for a co-pending PCT Application, PCT/US09/05346, was recently received. It identified the following references: U.S. Pat. Nos. 6,795,184; 7,274,450 and 6,798,511; and Published Applications Nos. US2004/0228371; US2007/0252992; US2006/0289761; US2007/0278407; US2007/0097373. Also identified were: a Ph.D. dissertation by Duerr, Erik Kurt, titled “Distributed Photomixers”, Mass. Inst. Tech., September 2002; and article thtled “Hole Diffusion Profile in a P—P+ Slicon Homojunction Determined by Terahertz and Midinfrared Spectroscopic Ellipsometry”, Hofmann et al., App. Phys. Lett., 95 032102 (2009).

The identified references, application Ser. No. 12/456,791, Provisional Application Ser. No. 61/208,735 Serial and No. 61/281,905, are all incorporated by reference into this Specification.

Even in view of relevant prior art, there remains need for an ellipsometer or polarimeter system for application in the Terahertz region, preferably in combination with a convenient approach to providing linearly polarized beams of electromagnetic radiation in which the azimuthal angle of the linear polarization can be controlled.

In very broad terms, the present invention is a terahertz ellipsometer or polarimeter system that, in a basic form, sequentially comprises:

Said terahertz ellipsometer or polarimeter system further comprises a first rotating element (RE1) and second rotating element (RE2) between said source and said detector of electromagnetic radiation, which can both be on the source or detector side of the stage (STG), but preferably has on thereof on each side.

The present invention is more specifically a terahertz ellipsometer or polarimeter system that sequentially comprises:

Said terahertz ellipsometer or polarimeter system further comprises a first rotating element (RE1) and second rotating element (RE2) between said backward wave oscillator (BWO) and said a Golay cell detector (DET) which can both be on the backward wave oscillator (BWO) or Golay cell detector (DET) side of the stage (STG), but preferably has on thereof on each side.

In use said backward wave oscillator (BWO) directs a beam (BI) of terahertz frequency electromagnetic radiation of a fundamental frequency to pass through said first rotatable polarizer comprising a wire grid (WGP1), then reflect from a sample (S) placed on said stage (STG) for supporting a sample, then pass through said second rotatable polarizer comprising a wire grid (WGP2), and, as output beam (BO) enter said Golay cell detector (DET) as output beam (BO), said beam also passing through the first (RE1) and second (RE2) rotating elements.

As alluded to, a preferred embodiment provides that said first rotating element (RE1) and second rotating element (RE2) are on the (BWO) and (DET) sides of said stage (STG) and sample, repectively, such that, in use, said backward wave oscillator (BWO) directs a beam (BI) of terahertz frequency electromagnetic radiation of a fundamental frequency to pass through said first rotatable polarizer comprising a wire grid (WGP1), then through said first rotating element (RE1), then reflect from a sample (S) placed on said stage (STG) for supporting a sample, then pass through said second rotating element (RE2), then pass through said second rotatable polarizer comprising a wire grid (WGP2), and, as output beam (BO) enter said Golay cell detector (DET) as output beam (BO).

Said terahertz ellipsometer or polarimeter system can provide that the first (RE1) and second (RE2) rotating elements are each selected from the group consisting of:

Said basic terahertz ellipsometer or polarimeter can further sequentially comprise:

Further, after said polarizer comprising a wire grid (WGP1) said terahertz ellipsometer or polarimeter can further comprise:

And, there can further sequentially be, after said second rotating element (RE2), a third concave parabolic mirror (PM3).

Also, further sequentially after said second rotatable polarizer comprising a wire grid (WGP2) there can be:

In use, with the foregoing additional elements in place, said backward wave oscillator (BWO) directs a beam (BI) of terahertz frequency electromagnetic radiation of a fundamental frequency to said frequency multiplier (FM), from which frequency multiplier (FM) a beam comprising a desired frequency is caused to be reflected from said first concave parabolic mirror (PM1) as a substantially collimated beam, said substantially collimated beam then being directed to reflect from said reflecting means (M1) and pass through said first rotatable polarizer comprising a wire grid (WGP1) and reflect from said second concave (PM2) parabolic mirror through said first rotating element (RE1), then reflect from a sample (S) placed on said stage (STG) for supporting a sample, then pass through said second rotating element (RE2), reflect from said third parabolic mirror (PM3), pass through said second rotatable polarizer comprising a wire grid (WGP2), then reflect from said fourth concave parabolic mirror (PM4) and enter said Golay cell detector (DET) as output beam (BO).

More simply, said basic terahertz ellipsometer or polarimeter can further comprise, between said backward wave oscillator (BWO) and said Golay cell detector (DET) at least one selection from the group consisting of:

More simply, said basic terahertz ellipsometer or polarimeter can further comprise a frequency multiplier (FM) following said backward wave oscillator (BWO).

Said basic terahertz ellipsometer or polarimeter can further comprise a chopper (CHP) between said backward wave oscillator (BWO) and said Golay cell detector (DET).

Said basic terahertz ellipsometer or polarimeter system can further comprise means for rotating, as a unit, said:

Said basic terahertz ellipsometer or polarimeter system can provide that the stage (STG) for supporting a sample (S) is oriented to support a sample in a substantially vertical plane, or in a substantially horizontal plane.

Where the stage is oriented substantially horizontally, system for enabling this can involve receiving a beam exiting said first rotating element (RE1) and directing it thereto via left and right vertical sequences, each of first (FLS/FRS), second (SLS/SRS) and third (TLS/TRS) elements, such that the terahertz frequence electromagnetic beam exiting said first rotating element reflects from the first left side element (FLS) to the second left side element (SLS), then to the third right side element (TRS), from which it is directed to reflect from a sample (S) placed on the stage (STG) in a substantially horizontal plane toward the third left side element (TLS), which reflects said beam to the second right side element (SRS) toward said first right side element (FRS), from which said beam is directed into said second rotating element (RE2).

Said terahertz ellipsometer or polarimeter system can involve a rotating polarizer that comprises a wire grid, selected from the group consisting of:

Said terahertz ellipsometer or polarimeter can further comprise at least one aperture (A) between said backward wave oscillator (BWO) and said Golay cell detector (DET).

It is also noted that said terahertz ellipsometer or polarimeter system can provide that the first (RE1) and second (RE2) rotating elements are rotated at relative speeds with respect to one another that form a ratio in the range of 1 to 10 or in the range of 10 to 1.

A method of determining physical and optical properties of samples using a terahertz frequency electromagnetic radiation utilizing a preferred embodiment of the present invention, comprises the steps of:

Said method continues with:

Said method can involve that the step of providing a terahertz ellipsometer or polarimeter system further comprises providing:

Said method can involve the sample (S) being oriented in a substantially vertical plane while data is obtained from said Golay cell detector (DET).

Said method can involve the sample (S) being oriented in a substantially horizontal plane, and a preferred approach by which this can be accomplished comprises application of a system comprising left and right vertical sequences of first (FLS/FRS), second (SLS/SRS) and third (TLS/TRS) elements, such that the terahertz frequence electromagnetic beam exiting said rotating polarizer comprising a wire grid (RWGP) reflects from the first left side element (FLS) to the second left side element (SLS), then to the third right side (TRS) element, from which it is directed to reflect from a sample (S) placed on the stage (STG) in a substantially horizontal plane toward the third left side (TLS) element, which reflects said beam to the second right side element (SRS) toward said first right side element (FRS), from which said beam is directed into said second rotating retarder (RE2).

Said method can further comprise providing means for rotating, as a unit, said:

Said method can further involve providing a chopper (CHP), said chopper (CHP) being a rotating wheel with a plurality of openings therein through which the terahertz electromagnetic radiation beam can pass, said chopper (CHP) being placed the locus of the terahertz electromagnetic radiation beam at some point between said backward wave oscillator and said Golay cell detector, and during the step d obtaining of data, causing said chopper to chop said terahertz frequency beam.

Said method can involve rotating the rotating polarizer comprising a wire grid (RWGP) and the rotating retarder (RRET) comprising first (RP), second (RM1), third (RM2) and fourth (RM3) elements, at relative speeds with respect to one another that form a ratio in the range of 1 to 10 or in the range of 10 to 1 during the step d obtaining of data.

Finally, said method can further comprise performing at least one selection from the group consisting of:

As additional support the following, which was previously disclosed in disclosed in a Co-Pending Parent Applications, Ser. Nos. 12/802,734 and 12/456,791, is provided to further disclose that the present invention comprises, or can further comprise a practical ellipsometer or polarimeter system for application in the range of frequencies between 300 GHz or below and proceeding well into and preferably through the Infrared frequency range. The prior art demonstrates that it is not unknown to propose, or provide a system for, and practice of ellipsometry at Terahertz (THz) frequencies, however, a specific embodiment than makes such possible and which is suitable for general application in universities and industry etc., has not been previously disclosed. To the Applicant's knowledge, there are no commercially available THz ellipsometers or polarimeters available in the market place. This is even more so the case where the ellipsometer or polarimeter also provides Infrared (IR) frequency capability.

While Synchrotrons have been used to provide THz frequency band electromagnetic radiation in ellipsometers, it is not remotely possible to provide a Synchrotron at every location whereat it is desired to practice THz ellipsometry. The present invention provides combination of many elements, which results in a novel, practical system for general application in the market place.

Before proceeding, it is of benefit to define some terminology. First, a generally accepted range for what constitutes a Terahertz range of frequencies is from 3×1011 (ie. 300 GHz), to 1.3×1012 (ie. 1.3 Thz), Hertz. The Terahertz range is sandwiched between the microwave, (the high end of which has a wavelength of 1 millimeter), and the far-infrared, (the long-wavelength edge of which is 100 micrometers), ranges of wavelengths/frequencies.

Next, it is noted that a number of sources of Terahertz (THz) electromagnetic radiation exit. For instance, a Smith-Purcell cell is a device which directs an energetic beam of electrons very close to a ruled surface of a diffraction grating. The effect on the trajectory of the beam is negligible, but a result is that Cherenkov radiation in the Terahertz frequency range can be created, where the phase velocity of the electromagnetic radiation is altered by the periodic grating. Another source of Terahertz radiation is a Free Electron Laser. In this source a beam of electrons is accelerated to relativistic speed and caused to pass through a periodic transverse magnetic field. The array of magnets is sometimes called an undulator or “wiggler” as it causes the electrons to form a sinusoidal path. The acceleration of he electrons causes release of photons, which is “synchrotron radiation”. Further, the electron motion is in phase with the field of said released electromagnetic radiation, and therefore the fields add coherently. Instabilities in the electron beam resulting from interactions of the oscillations in the undulators lead to emission of electromagnetic radiation, wherein electrons radiate independently. The wavelength of the emitted electromagnetic radiation from the electrons can be adjusted by adjusting the energy of the electron beam and/or magnetic field strength of the undulators, to be in the Terahertz range. Another source of Terahertz frequencies is a Backward Wave Oscillator (BWO), which is a vacuum tube system comprising an electron gun that generates an electron beam and causes it to interact with an electromagnetic wave traveling in a direction opposite to that of ejected electrons such that THz frequency oscillations are sustained by interaction between the propagating traveling wave backwards against the electron beam.

It is also disclosed that numerous detectors exist for monitoring Terahertz range electromagnetic radiation. One example is a Golay cell which operates by converting a temperature change resulting from electromagnetic radiation impinging onto material, into a measurable signal. Generally, when electromagnetic radiation is caused to impinge on a blackened material it heats a gas, (eg. Xenon) in an first chamber of an enclosure, and that causes a distortable reflecting diaphram/film adjacent to said first chamber to change shape. In a second chamber, separated from the first by said diaphram/film an electromagnetic beam is caused to reflect from the film and into a photocell, which in turn converts the received electromagnetic radiation into an electrical signal. A Bolometer is another detector of monitoring Terahertz range electromagnetic radiation, but operates by using the effect of a changing electric resistance caused by electromagnetic radiation impinging onto a blackened metal.

It is also noted that there are Solid State sources and detectors of Terahertz frequency electromagnetic radiation. For instance, an identified reference by Nagashima et al. discloses that THz pulses can be generated by a bow-tie photoconductive radiation antenna excited by a mode-locked Ti-saphire laser with 80 Fs time width pulses, and a detection antenna can be formed from a dipole-type photoconductive antenna with a 5 micron gap fabricated on thin film LT-GaAs. Further, it is known that a company named AB Millimeter in Paris France, supplies a system that covers the entire range from 8 GHz to 1000 GHz with solid state source and detector devices.

With the above insight, it is disclosed that the present invention can comprise an ellipsometer or polarimeter system which comprises a selection from the group consisting of:

Said ellipsometer or polarizer system further comprises, between said THz source and said detector, at least one selection from the group:

It is noted that the polarization state generator comprising a THz source of electromagnetic radiation that provides substantially polarized output in a frequency range between 300 GHz or lower and extending higher than at least 1 THz, utilizes natural polarization provided by the THz source and does not require use of a separate polarizer; whereas said source of electromagnetic radiation in functional combination with a polarization state generator that provides substantially polarized output in a frequency range between 300 GHz or lower and extending higher than at least 1 THz, typically comprises a separate polarizer.

Continuing, the THz source of electromagnetic radiation can comprise at least one selection from the group consisting of:

Further, the ellipsometer or polarimeter system preferably comprises at least one odd-bounce polarization state rotation system present between:

Coupling the odd bounce optical image rotating system with a substantially linear polarizing element, (which can comprise a source of unpolarized electromagnetic radiation and a polarizer, or can comprise a source that provides polarized electromagnetic radiation at its output), provides a polarizer system in which the polarizing element can remain stationary while the azimuthal angle of the polarized beam of electromagnetism exiting therefrom, (as viewed from a position along the locus of an electromagnetic beam caused to enter thereto), is rotated.

For general insight, it is also noted that a single three-hundred-sixty (360) degree rotation of a present invention odd bounce optical image rotating element system about an axis coincident with a beam of electromagnetic radiation which functionally passes therethrough, causes seven-hundred-twenty (720) degrees of rotation of the major intensity orthogonal component. This is not of any critical consequence, but is mentioned as it must be taken into account during practice of present invention methodology.

The detector of electromagnetic radiation in a range between 300 GHz or lower and extending higher than 1 THz, can be a selection from the group consisting of:

Further, said ellipsometer or polarimeter system further comprises an FTIR source and a detector for detecting said FTIR frequency output in a frequency range above about 1 THz, and means for selecting between:

The detector for detecting said FTIR frequency output in a frequency range above about 1 THz, and in which said detector of electromagnetic radiation in a range between 300 GHz or lower and extending higher than at least 1 THz, are each independently selected from the group:

As mentioned, in a preferred embodiment, the ellipsometer or polarimeter system has output from said THz source, preferably with a frequency multiplier in functional combination, so that it overlaps output from said FTIR source in frequency, between at least 1.0 to 1.4 THz. And preferably said sources are calibrated such that substantially the same results, (eg. ellipsometric PSI and/or DELTA), are achieved by analyzing output from either of the selected detectors in the frequency range of between about 1.0 to 1.4 THz.

In more detail, a preferred present invention ellipsometer or polarimeter system comprises:

Further, said ellipsometer or polarimeter comprises means for selecting between said THz and FTIR sources.

Said ellipsometer or polarimeter further comprises:

Said preferred ellipsometer or polarization system embodiment further comprises at least one odd-bounce polarization state rotation system present between:

In use a selected functional combination of selected source and selected detector is applied to cause electromagnetic radiation to impinge on and interact with a sample on said sample support, then enter said selected detector, to the end that said detector produces an output.

Again, said preferred embodiment provides, that the output from the functional combination of said selected THz source and preferably a frequency multiplier, and that from said FTIR source overlap in frequency between at least 1.0 to 1.4 THz such that substantially the same results, (eg. ellipsometric PSI and/or DELTA), are achieved by analyzing output from either of the selected detectors in the frequency range of between about 1.0 to 1.4 THz.

A preferred present invention system also comprises a chopper for chopping the electromagnetic beam which interacts with the sample. (It is noted that FTIR Sources provide a natural “chopping” effect by way of a moving mirror therewithin, hence, an added chopper is relevant only when a THZ Source is selected). Further, a chopper is typically applied when other elements are caused to rotate during data acquisition. Use of a chopper enables noise reduction, particularly where data is obtained with the system located in a non-darkened room, such that spurious electromagnetic radiation is present.

A present invention method of characterizing a sample comprises the steps of:

A) providing an ellipsometer or polarimeter as described above;

B) selecting a source and detector;

C) applying said selected source to cause substantially polarized electromagnetic radiation to impinge on and interact with said sample on said sample support, then proceed to and enter said selected detector, to the end that said detector provides output.

The present invention method also preferably involves chopping the substantially polarized electromagnetic radiation which is caused to impinge on and interact with said sample on said sample support, and which then proceeds to and enters said selected detector, to the end that said detector provides output based substantially only on the chopped beam content.

And, said method can further comprise performing at least one selection from the group consisting of:

Said method can further comprise the step of continuously or step-wise rotating at least one of the at least one odd-bounce polarization state rotation system present between said source and detector, or operating a present electro, acousto or opto-modulator, during data acquisition.

The benefit is that, especially in ellipsometer/polarimeter etc. systems which operate in the IR range of wavelengths and below, it can be difficult to cause rotation of a linear polarizer, (or analyzer), without adversely causing deviation of a beam of electromagnetic radiation caused to pass therethrough, or causing mis-coordination of multiple elements thereof, (ie. multiple tipped wire linear polarizer as described in U.S. Pat. No. 5,946,098). The present invention allows setting fixed substantially linear polarizer, and analyzer azimuthal orientations, and using the odd bounce optical image rotating element instead, to effect different electromagnetic beam azimuthal rotation orientations.

It is also noted that various selected combinations of elements that comprise an ellipsometer or polarimeter, such as a specific selection from:

At the time of this submittal it is believed that a preferred embodiment makes use of a backward wave oscillator (BWO) in combination with a multiplier that provides ×1, ×2 ×3 ×6 and ×9 capability, in functional combination with Golay cell or bolometer, provides good results in the range of from about 0.12-1.5 THz. Further, a conventional FTIR Source as used in a J. A. Woollam Co. IR-VASE®, to provide 10-150 THz capability, has been shown capable of providing output down to about 1.0 Thz. This beneficially allows an overlap between the THz and IR sources between about 1.0 and 1.4 Thz, which can be used for verification of results separately obtained using the THz and IR sources. In addition, it can be advantagous to cool a detector, (eg. by use of liquid helum), and to adjust beam chopper rate, (eg. between about 12-50 Hz), differently for different source and detector combinations.

It is further believed that a present invention ellipsometer or polarimeter system which comprises:

In addition, present invention methodology which involves which the step of providing an ellipsometer or polarimeter system involves the selection of:

This is the case wherein during data collection said odd-bounce optical image rotating system is rotated as a selection from the group consisting of:

Additional basis of Patentability is more particularly provided when the system comprises at least two rotating elements, each thereof being selected from the group consisting of:

It is also presented that an ellipsometer or polarimeter system which operates in the THz range, and its method of use, which ellipsometer or polarimeter comprises a chopper to chop the electromagnetic beam and provide substantially only the chopped electromagnetic beam to the detector, and which is in functional combination with at least two rotating elements, each thereof being selected from the group consisting of:

Continuing, the foregoing was substantially disclosed in Co-Pending Pending application Ser. No. 12/456,791 Filed Jun. 23, 2009. In the following, variations on the foregoing, substantially as disclosed in Provisional Application Ser. No. 61/281,905 Filed Nov. 22, 2009, are discussed.

Much as in the foregoing, a present invention ellipsometer or polarimeter system comprises:

a) a source selected from the group consisting of:

One difference between that disclosed above, and what is now disclosed, is that the presently disclosed system provides that said polarizatiom state generator is selected from the group consisting of:

As in the foregoing, a present invention ellipsometer or polarimeter system further comprises:

and a source selected from the group consisting of:

Another difference between what was disclosed above and what is now disclosed is that the presently disclosed system provides that said polarization state generator is selected from the group consisting of:

As in the foregoing disclosure,

This is followed by:

And said ellipsometer or polarimeter system again further comprises, between said selected source and said selected detector, at least one selection from the group:

In use a selected functional combination of selected source, optional polarization state generator, and detector is applied to cause electromagnetic radiation to pass impinge on and interact with a sample on said sample support (S), then enter said selected detector (D1) (D2) (D3), to the end that said detector produces an output.

A specific presently disclosed invention is found where the A2 polarization state generator comprises an FTIR source (S2), and the A4 polarization state generator comprises a THz source (S1), wherein a22 and a42 are further elected.

Another presently disclosed invention is found where the A2 polarization state generator comprises an FTIR source (S2), and the A4 polarization state generator comprises a THz source (S1), wherein a21 and a41 are further elected.

Another presently disclosed invention is found where the A2 polarization state generator comprises an FTIR source (S2), and the A4 polarization state generator comprises a THz source (S1), wherein a21 and a42 are further elected.

Another presently disclosed invention is found where the A2 polarization state generator comprises an FTIR source (S2), and the A4 polarization state generator comprises a THz source (S1), wherein a22 and a41 are further elected.

A method of characterizing a sample comprising the steps of:

Another recitation of a presently disclosed invention is that it is an ellipsometer or polarimeter system comprising:

This is followed by:

Between said source and said detector, there is also present at least one selection from the group:

It is noted that the polarization state generator characterized by a selected odd-bounce polarization state rotation system followed by said polarization state generator exit polarizer operates by the odd-bounce polarization state generator receiving an at least partially polarized beam of electromagnetic radiation from the source thereof, rotating the polarization state of said at least partially polarized beam and and passing it through said polarization state exit polarizer which serves to improve the purity of the polarization state exiting therefrom.

It is also noted that the polarization state generator is characterized by a polarization state generator entry polarizer followed by said polarization state generator exit polarizer operates by the polarization state generator entry polarizer receiving an at least partially polarized beam of electromagnetic radiation from the source thereof and then passing it through said polarization state exit polarizer. Said polarization state generator entry polarizer serves to enable avoiding a condition wherein an effective azimuth of the at least partially polarized beam of electromagnetic radiation provided by the source thereof, and that of the polarization state generator exit polarizer present at essentially 90 degrees with respect to one another thereby preventing the at least partially polarized beam of electromagnetic radiation from progressing beyond the polarization state generator exit polarizer.

Another recitation of a present invention ellipsometer or polarimeter system provides that it comprise:

Said elements are followed by:

In addition to said polarization state generator components, said ellipsometer or polarimeter system further comprises, between said source and said detector, at least one selection from the group:

Another recitation of a present invention ellipsometer or polarimeter system provides that it comprise:

Said ellipsometer or polarimeter system then further comprises:

In addition to said polarization state generator components, said ellipsometer or polarimeter system further comprises, between said source and said detector, at least one selection from the group:

Continuing, the present invention ellipsometer and polarimeter system can be configured as a Rotating Analyzer, a Rotating Polarizer or a Rotating Compensator system. The preprint paper in the Background Section discloses a Rotating Analyzer system. Reference to FIG. 1p shows that present invention Rotating Analyzer ellipsometer or polarimeter system sequentially comprises:

In use a polarized beam of Terahertz spectral range electromagnetic radiation is provided by said backward wave oscillator, is focused by the focusing lens, has its polarization state rotated by said rotatable image rotation system and passes through said rotatable wire grid polarizer, then impinges on a sample placed on said sample supporting stage, reflects therefrom and passes through said rotating analyzer and enters said Golay cell. Said Rotating Analyzer ellipsometer or polarimeter system is distinguished in that, during data acquisition, the rotatable image rotation system and rotatable wire grid polarizer are functionally stepwise rotated in tandum, wherein said rotatable wire grid polarizer is stepwise rotated through a sequence of angles twice that of the rotatable image rotation system, such that the polarization state of the beam provided to the wire grid polarizer by the rotatable image rotation system, is passed by said rotatable wire grid polarizer even where the polarization state of the polarized beam of Terahertz spectral range electromagnetic radiation from the backward wave oscillator is rotated by 90 degrees.

Said Rotating Analyzer ellipsometer or polarimeter system can be characterized by said rotatable image rotation system being an odd bounce (OB) (OB′) optical image rotating system comprising an odd number of at least three reflective elements oriented such that a beam of electromagnetic radiation provided by said source of electromagnetic radiation interacts with each of said at least three reflective elements of said at least one odd bounce optical image rotating system and exits therefrom along a non-deviated non-displaced trajectory, said beam of electromagnetic radiation also interacting with a sample system placed on said stage for supporting a sample system, and said analyzer before entering said detector, and the at least one odd bounce (OB) (OB′) optical image rotating system can consist of a selection from the group consisting of:

Said present invention Rotating Analyzer ellipsometer or polarimeter system can further comprise at least one beam directing reflecting means and the sample supporting stage can be part of a 20 goniometer.

A variation on the present invention Rotating Analyzer ellipsometer or polarimeter system can sequentially comprise:

Said ellipsometer or polarimeter system further comprises:

In use a polarized beam of Terahertz spectral range electromagnetic radiation is provided by said backward wave oscillator, is optionally focused by the focusing lens, has its polarization state rotated by said rotatable image rotation system and passes through said rotatable wire grid polarizer, then impinges on a sample placed on said sample supporting stage, reflects therefrom and passes through said rotating analyzer and enters said Golay cell.

Said ellipsometer or polarimeter system is distinguished in that, during data acquisition, the rotatable image rotation system and rotatable wire grid polarizer are functionally stepwise rotated in tandum, wherein said rotatable wire grid polarizer is stepwise rotated through a sequence of angles twice that of the rotatable image rotation system, such that the polarization state of the beam provided to the wire grid polarizer by the rotatable image rotation system, is passed by said rotatable wire grid polarizer even where the polarization state of the polarized beam of Terahertz spectral range electromagnetic radiation from the backward wave oscillator is rotated by 90 degrees.

Said ellipsometer or polarimeter system can involve a rotatable image rotation system which is an odd bounce (OB) (OB′) optical image rotating system comprising an odd number of at least three reflective elements oriented such that a beam of electromagnetic radiation provided by said source of electromagnetic radiation interacts with each of said at least three reflective elements of said at least one odd bounce optical image rotating system and exits therefrom along a non-deviated non-displaced trajectory, said beam of electromagnetic radiation also interacting with a sample system placed on said stage for supporting a sample system, and said analyzer before entering said detector.

Said ellipsometer or polarimeter system at least one odd bounce (OB) (OB′) optical image rotating system can consist of a selection from the group consisting of:

Said ellipsometer or polarimeter system can further comprise at least one beam directing reflecting means.

Said ellipsometer or polarimeter system can involve a sample supporting stage is part of a system for controlling the angle of incidence at which a beam of electromagnetic radiation is caused to approach said sample.

Another recitation of a rotating analyzer ellipsometer or polarimeter system provides that it can sequentially comprise:

Said ellipsometer or polarimeter system further comprises:

In use a polarized beam of Terahertz spectral range electromagnetic radiation is provided by said backward wave oscillator, is optionally focused by the focusing lens, has its polarization state altered by said first rotatable wire grid polarizer and then by said second rotatable wire grid polarizer, then impinges on a sample placed on said sample supporting stage, reflects therefrom and passes through said rotating analyzer and enters said Golay cell.

Said ellipsometer or polarimeter system is distinguished in that said two rotatable wire grid polarizers are functionally operated in tandum such that the polarization state of the beam provided to the second rotatable wire grid polarizer by the first rotatable wire grid polarizer, is passed by said second rotatable wire grid polarizer, where it not be passed were the first rotatable wire grid polarizer not present and the polarization state of the polarized beam of Terahertz spectral range electromagnetic radiation from the backward wave oscillator is rotated by 90 degrees at the location of said sample.

Said ellipsometer or polarimeter system can further comprise at least one beam directing reflecting means.

Said ellipsometer or polarimeter system can involve a sample supporting stage is part of a system for controlling the angle of incidence at which a beam of electromagnetic radiation is caused to approach said sample.

FA

A fixed analyzer ellipsometer or polarimeter system can sequentially comprise:

Said ellipsometer or polarimeter system further comprising:

In use a polarized beam of Terahertz spectral range electromagnetic radiation is provided by said backward wave oscillator, is optionally focused by the focusing lens, optionally has its polarization state rotated by said rotatable or rotating polarizer, then impinges on a sample placed on said sample supporting stage, reflects therefrom and passes through said rotatable image rotation system and fixed position analyzer and enters said Golay cell.

Said ellipsometer or polarimeter system is distinguished in that, during data acquisition, the rotatable image rotation system is stepwise rotated while the analyzer remains fixed in position.

A present invention Rotating Polarizer ellipsometer or polarimeter system sequentially can comprise:

RP

Said ellipsometer or polarimeter system can further comprise:

In use a polarized beam of Terahertz spectral range electromagnetic radiation is provided by said backward wave oscillator, is optionally focused by the focusing lens, has its polarization state rotated by said rotatable or rotating polarizer, then impinges on a sample placed on said sample supporting stage, reflects therefrom and passes through said rotatable image rotation system and rotatable wire grid analyzer and enters said Golay cell.

Said ellipsometer or polarimeter system is distinguished in that, during data acquisition, the rotatable image rotation system and rotatable wire grid analyzer are functionally stepwise rotated in tandum, wherein said rotatable wire grid analyzer is stepwise rotated through a sequence of angles twice that of the rotatable image rotation system, such that the polarization state of the beam provided, to the rotatable wire grid analyzer by the rotatable image rotation system.

Said ellipsometer or polarimeter system can involve a rotatable image rotation system is an odd bounce (OB) (OB′) optical image rotating system comprising an odd number of at least three reflective elements oriented such that a beam of electromagnetic radiation provided by said source of electromagnetic radiation interacts with each of said at least three reflective elements of said at least one odd bounce optical image rotating system and exits therefrom along a non-deviated non-displaced trajectory, said beam of electromagnetic radiation also interacting with a sample system placed on said stage for supporting a sample system, and said analyzer before entering said detector.

Said at least one odd bounce (OB) (OB′) optical image rotating system can consist of a selection from the group consisting of:

Said ellipsometer or polarimeter system can further comprise at least one beam directing reflecting means.

Said ellipsometer or polarimeter system can provide that the sample supporting stage is part of a system for controlling the angle of incidence at which a beam of electromagnetic radiation is caused to approach said sample.

A present invention Rotating Compensator ellipsometer or polarimeter system sequentially comprising:

RC

Said ellipsometer or polarimeter can system further comprise:

In use a polarized beam of Terahertz spectral range electromagnetic radiation is provided by said backward wave oscillator, is optionally focused by the focusing lens, has its polarization state rotated by said rotatable image rotation system and passes through said rotatable wire grid polarizer, then impinges on a sample placed on said sample supporting stage, reflects therefrom and passes through said rotatable analyzer; said Terahertz spectral range electromagnetic radiation also passing through said optical chopper and rotating compensator; and enters said Golay cell.

Said ellipsometer or polarimeter system is distinguished in that, during data acquisition while said rotating compensator is caused to continuously rotate, the rotatable image rotation system and rotatable wire grid polarizer are functionally stepwise rotated in tandum, wherein said rotatable wire grid polarizer is stepwise rotated through a sequence of angles twice that of the rotatable image rotation system, such that the polarization state of the beam provided to the wire grid polarizer by the rotatable image rotation system, is passed by said rotatable wire grid polarizer even where the polarization state of the polarized beam of Terahertz spectral range electromagnetic radiation from the backward wave oscillator is rotated by 90 degrees

Said ellipsometer or polarimeter system can provide that the rotatable analyzer is optionally also stepwise rotated during data acquisition.

Said ellipsometer or polarimeter system can provide that said rotatable image rotation system is an odd-bounce (OB) (OB′) optical image rotating system comprising an odd number of at least three reflective elements oriented such that a beam of electromagnetic radiation provided by said source of electromagnetic radiation interacts with each of said at least three reflective elements of said at least one odd bounce optical image rotating system and exits therefrom along a non-deviated non-displaced trajectory, said beam of electromagnetic radiation also interacting with a sample system placed on said stage for supporting a sample system, and said analyzer before entering said detector.

Said at least one odd bounce (OB) (OB′) optical image rotating system consists of a selection from the group consisting of:

Said ellipsometer or polarimeter system can further comprise at least one beam directing reflecting means.

Said ellipsometer or polarimeter system can provide that the sample supporting stage is part of a system for controlling the angle of incidence at which a beam of electromagnetic radiation is caused to approach said sample.

Said ellipsometer or polarimeter system can provide that the rotating compensator is present at a selection from the group consisting of:

As further, generalized, disclosure it is presented that a TeraHertz Ellipsometer can be configured from components:

Source 1=Generalized Narrow-Band Essentially Single Frequency:

Source 2=Generally Broadband Blackbody Dominated:

Frequency Purification Systems

THZ Filter 1+Narrow Pass THZ Filter

THZ Filter 2+Order Sorting

THZ Filter 3

DET 1=

DET 2=

DET 3=

Changing and element, (stepwise of continuous), provides synchronization to:

From the above elements two types of THZ Ellipsometer Systems can be configured, namely:

Scanning Monochromator

REQUIRED SOURCE 1

OPTIONAL THZ FILTER 3

Dual System: Scanning+FTIR System

The foregoing outline provides basis for describing specific present invention systems.

First, a scanning monochromater system for application in the Tarahertz frequency range, can comprise:

a narrow-band essentially single frequency source selected from the group consisting of:

Said scanning monochromater system can further comprise at least one selection from the group:

Said scanning monochromater system can further comprise at least one polarization state rotating system between said selected source and selected detector.

Said scanning monochromater system can comprise two polarization state rotating systems between said selected source and selected detector.

Said scanning monochromater system can further comprise a beam chopper, said beam chopper being applied to chop said beam of electromagnetic radiation during use.

Said scanning monochromater system can, during use, cause said electromagnetic beam to be chopped by said beam chopper while two elements selected from the group consisting of:

Said scanning monochromater system can further comprise means for controlling the angle of incidence at which said beam of electromagnetic radiation from said selected source approaches said sample.

Said scanning monochromater system can further comprise, between said selected source and selected detector, at least one terahertz filter and narrow pass THZ filter selected from the group:

Said scanning monochromater system can further comprise a rotatable polarizer, the rotation of which is synchronized to that of the said at least one polarization state rotating system between said selected source and selected detector.

Said scanning monochromater system can further comprise a lock-in system referenced to said at least one component selected from the group of said:

Another present invention system is a dual scanning and FTIR system for application in the Terahertz and Infrared frequency range, comprising:

Said dual scanning and FTIR system for application in the Terahertz and Infrared frequency range can further comprise, in combination with the selected source for providing Thz range electromagnetic radiation which is selected from the group consisting of:

Said dual scanning and FTIR system for application in the Terahertz and Infrared frequency range can further comprise a fixed stokes vector setting subsystem polarizer or partial polarizer positioned in the path of at least one electromagnetic beam from a selection from the group consisting of:

Said dual scanning and FTIR system can further comprise a second fixed stokes vector setting sub-system polarizer or partial polarizer positioned in the path of at least one electromagnetic beam from a selection from the group consisting of:

Said dual scanning and FTIR system for application in the Terahertz and Infrared frequency range can further comprise at least two rotating elements, selected from the group:

Said dual scanning and FTIR system for application in the Terahertz and Infrared frequency range can further comprise an ISVC fixed stokes vector control selecting sub-system polarizer or partial polarizer positioned in the path of at least one electromagnetic beam from a selection from the group consisting of:

Said dual scanning and FTIR system for application in the Terahertz and Infrared frequency range can further comprise at least one polarization state rotating system between said selected source and selected detector positioned in the path of at least one electromagnetic beam from a selection from the group consisting of:

Said dual scanning and FTIR system for application in the Terahertz and Infrared frequency range can further comprise a second polarization state rotating system between said selected source and selected detector positioned in the path of at least one electromagnetic beam from a selection from the group consisting of:

Said dual scanning and FTIR system can, during use, provide that said electromagnetic beam is caused to be chopped by a beam chopper while two elements selected from the group consisting of:

Said dual scanning and FTIR system can further comprise means for controlling the angle of incidence at which said beam of electromagnetic radiation from said selected source approaches said sample.

Said scanning monochromater system can further comprise a rotatable polarizer, the rotation of which is synchronized to that of the said at least one polarization state rotating system between said selected source and selected detector.

Said dual scanning and FTIR system can further comprise a lock-in system referenced to said at least one component selected from the group:

The present invention will be better understood by reference to the Detailed Description Section of this Specification, in combination with the Drawings.

FIGS. 1a-1c show demonstrative configurations for a present invention ellipsometer or polarimeter system.

FIG. 1d shows an alternative polarization state generator involving a modulator.

FIGS. 1e-1g show systems similar to those in FIGS. 1a-1c, with the relative positions of the Odd Bounce image rotation system and Polarizer reversed.

FIG. 1h indicate that the Odd Bounce image rotation system Polarizer reversed are controlled in synchrony.

FIGS. 1i-1k are similar to FIGS. 1e-1g, but with the Odd Bounce image rotation system replaced with a second Polarizer.

FIGS. 1l-1o demonstrate various element configurations for a Terahertz ellipsometer or polarimeter.

FIG. 1p shows specific Terahertz ellipsometer or polarimeter.

FIGS. 2a-2d show various aspects of Therahertz frequency Sources.

FIGS. 2e-2g show a demonstrative detectors of Terahertz frequencies.

FIG. 3a demonstrates an Odd Bounce image rotating system comprising three (3) reflecting elements.

FIG. 3b demonstrates an Odd Bounce image rotating system comprising five (5) reflecting elements.

FIG. 4 demonstrates a preferred compensator (C) (C′) (C″) which has been used in a rotating compensator ellipsometer system for application in the IR range of wavelengths.

FIG. 5a demonstrates a combined Non-Brewster Angle and Brewster Angle Polarizer system.

FIG. 5b demonstrates a dual tipped wire grid polarizer system.

FIG. 6 demonstrates data which can be achieved by application of the Present Invention, including in an overlap frequency range between about 1.0 and 1.4 THz.

FIG. 7 demonstrates displaying data obtained by practice of the present invention using a computer.

FIG. 8a shows a preferred embodiment of a present invention THZ ellipsometer or polarimeter.

FIG. 8a′ shows a more detailed preferred embodiment of a present invention THZ ellipsometer or polarimeter.

FIG. 8b shows that the FIG. 8a preferred embodiment of a present invention THZ ellipsometer or polarimeter can be rotated to enable achieving different angles-of-incidence (AOI).

FIG. 9 shows a system for enabling the present invention FIGS. 8a and 8b embodiments to be applied to investigating samples on a horizontally oriented stage.

FIG. 10a shows an embodiment of the FIGS. 8a and 8b rotating retarder (RRET).

FIG. 10b shows a preferred embodiment of the FIGS. 8a and 8b rotating retarder (RRET).

FIGS. 10c-10e show additional embodiments of the FIGS. 8a and 8b rotating retarder (RRET).

At the outset attention is directed to FIG. 8a, which shows a preferred present invention Terahertz Ellipsometer sequentially system comprising:

Said terahertz ellipsometer or polarimeter system further comprises a first rotating element (RE1) and second rotating element (RE2) between said source and detector of electromagnetic radiation.

In use said source of terahertz electromagnetic radiation directs a beam (BI) of terahertz frequency electromagnetic radiation of a fundamental frequency to pass through said first rotatable polarizer, then reflect from a sample (S) placed on said stage (STG) for supporting a sample, then pass through said second rotatable polarizer, and as output beam (BO) enter said detector of electromagnetic radiation as output beam (BO), wherein said beam also passes through said first rotating element (RE1) and second rotating element (RE2).

FIG. 8a′ shows a more detailed preferred presently disclosed terahertz ellipsometer sequentially system comprising:

Assuming optional elements are present, in use said backward wave oscillator (BWO) directs a beam of terahertz frequency electromagnetic radiation of a fundamental frequency to said frequency multiplier (FM), from which frequency multiplier (FM) a beam comprising a desired frequency is caused to be reflected from said first concave parabolic mirror (PM1) as a substantially collimated beam, said substantially collimated beam then being directed to reflect from said reflecting means (M1) and pass through said first rotatable wire grid polarizer (WGP1) and reflect from said second concave parabolic mirror (PM2) through said rotating wire grid polarizer (RWGP), then reflect from a sample (S) placed on said stage (STG) for supporting a sample, then pass through said rotating retarder (RRET), reflect from said third parabolic mirror (PM3), pass through said second rotatable wire grid polarizer (WGP2), then reflect from said fourth concave parabolic mirror (PM4) and enter said golay cell detector (DET).

FIG. 8b shows that that the FIGS. 8a and 8a′ terahertz ellipsometer system can further comprise means for rotating, as a unit, said:

FIG. 8b is to also be interpreted to, in addition, or as an option, enable said terahertz ellipsometer system to further comprise means for rotating, as a unit, said:

In practice either the components on the Source (BWO) and/or Detector (DET) side of the Stage (STG), along with the stage can be rotated to set an Angle-of-Incidence of a Terahertz beam onto a sample.

The terahertz ellipsometer system can further comprise a beam chopper (CHP), said beam chopper (CHP) being of any functional design, but typically being a rotating wheel with a plurality of openings therein through which the terahertz electromagnetic radiation beam can pass, said chopper being placed the locus of the terahertz electromagnetic radiation beam at some point between said backward wave oscilator and said golay cell detector, said wheel being made from high density polyethelyene. Note the position of the chopper (CH) in FIG. 8a′ is demonstrative, not limiting. The chopper (CHP) can be located at any functional location in the terahertz ellipsometer system.

It is noted that said terahertz ellipsometer system is typically oriented to mount samples (S) to said stage (STG) for supporting a sample so that said sample (S) is in a vertical plane as observed in labratory coordinates. FIG. 9 shows a system that allows said terahertz ellipsometer system to orient the stage (STG) for supporting a sample (S) in a horizontal plane. Note that the stage (STG) for supporting a sample (S) is oriented to support a sample in a horizontal plane and in which the beam is directed thereto via left and right vertical sequences, each of first (FLS/FRS) second (SLS/SRS) and third (TLS/TRS) elements, such that the terahertz frequence electromagnetic beam exiting said rotating wire grid polarizer (RWGP) reflects from the first left side element (FLS) to the second left side element (SLS), then to the third right side element (TRS), from which it is directed to reflect from a sample (S) placed on the stage (STG) in a horizontal plane toward the third left side element (TLS), which reflects said beam to the second right side element (SRS) toward said first right side element (FRS), from which said beam is directed into said rotating retarder (RRET), (see FIG. 8a).

It is noted that in use the terahertz ellipsometer system rotating wire grid polarizer (RWGP) and the rotating retarder (RRET) comprising first (RP), second (RM1), third (RM2) and fourth (RM3) elements are preferably, but not necessarily, rotated at relative speeds with respect to one another that form a ratio in the range of of 1 to 10 or 10 to 1.

FIG. 10a shows that the terahertz ellipsometer system rotating retarder (RDT) can comprise a prism (RP), which receives a beam oriented perpendicular to a first side thereof and exits a reflected beam oriented perpendicular to a second side thereof, said reflection being a total internal reflection from a side oriented at forty-five degree angles to said first and second sides, is positioned to be the first element the terahertz frequence electromagnetic beam encounters. Also shown present are reflecting elements (RM1) (RM2) and (RM3) to provide a four element rotating retarder, which it is mentioned, is functionally equivalent to a ½ wave plate. It is also noted that, while not preferred, the positions of (RP), and any one of the (RM1) (RM2) (RM3) can be swapped and a retarder (RET) which can be applied in use still results.

FIG. 10b shows a preferred rotating retarder (RRET) comprising, in any functional order, first (RP), second (RM1), third (RM2) and fourth (RM3) reflective elements from each of which, in use, an electromagnetic beam reflects once, said first reflective element (RP) being prism (RP) which receives a beam through a first side thereof and exits a reflected beam through a third side thereof, said reflection being from a second side thereof oriented at prism forming angles to said first and third sides; said elements (RP) (RM1) (RM2) (RM3) being oriented with respect to one another such that the locus of the beam reflecting from the second side of said prism approaches said second reflective side thereof at an angle equal to or greater than that required to achieve total internal reflection within said prism (RP), and such that the locus of beam reflected from the fourth element in the sequence of elements is substantially colinear and without deviation or displacement from the locus of the beam received by the first element in said sequence of elements.

FIGS. 10c-10e indicate that while the FIG. 10a embodiment is preferred, any functional order of the first (RP), second (RM1), third (RM2) and fourth (RM3) reflective elements can be applied in any functional order. Again, said first reflective element (RP) is a prism in which total internal reflection occurs.

Turning now to previously disclosed Drawings that are included for support of the present preferred embodiment of the invention shown in FIGS. 8a-10d, FIGS. 1a, 1b and 1c show various approaches to providing a THZ Ellipsometer System. FIG. 1a shows Three Sources (S1) (S2) (S3), which can each be a backward wave oscillator or a Smith-Purcell cell or a free electron laser or a solid state device. Also demonstrated are Beam Combiners (BC1) (BC2) (BC3) which serve to direct electromagnetic radiation from Sources (S1) (S2) S3), respectively, toward a Sample (S), via optional Polarizer (P), (the natural source polarization can suffice), Odd Bounce Image Rotating System (OB) and Compensator (C). Said optional (P) (OB) (C) components are shown as typically, in combination, being termed a Conventional Polarization State Generator (CPSG) and are included to polarize a beam of electromagnetic radiation provided by a Source (S1) (S2) S3). It is possible, however, that a selected Source (S1) (S2) S3) can provide a beam of electromagnetic radiation which is already polarized, therefore, in this Specification it is to be understood that it is within the definition of “Polarization State Generator (PSG)” that it comprise the Source (S1) (S3) S3) with or without the presence of Conventional Polarization State Generator (CPSG) components. FIG. 1a also shows that optional (OB′) (C′) and (P) components between the Sample (S) and a Detector (D1) D2). Note that Detectors (D1) and (D2) have electromagnetic radiation directed thereinto by Beam Splitters/Directors. In use Source (S1) (S3) and (S3) can be energized or not so that a beam of electromagnetic radiation progressing toward the Sample (S) comprises various ranges of wavelengths. For instance, Source (S1) can be selected to provide Terahertz (Thz) frequencies, and Source (S3) selected to provide Infrared (IR) frequencies, and during use one or the other can be energized so that only (THz) or (IR) wavelengths are provided, or both can be energized to provide a broad combined range of wavelengths, preferable with an overlap range of between about 1.0 Thz, and 1.4 Thz or higher, frequency. The same general description of FIG. 1a applies to FIGS. 1b and 1c, with the exception that the Sources and Detectors are shown as configured differently. In FIG. 1b the Sources (S1) (S3) (23) and Detectors (D1) (D2) (D3) are simply sequentially slid into position. In FIG. 1c, Input Beam Reflecting Means (BRI) and Output Beam Reflecting Means (BRO) are shown as being rotatable to selectively direct electromagnetic radiation from one source or another toward the Sample (S). The configurations shown in FIGS. 1a-1c are not to be considered limiting, but rather are demonstrative. For instance, it is possible to choose a FIG. 1a Source selection approach, and a FIG. 1b or 1c Detector selection arrangement etc. And it is possible to provide only one Source, (ie. a Therahertz frequency providing system), while providing a selection between two Detectors (eg. a Golay cell or Bolometer).

It is also noted that the configuration in FIG. 1a can be operated with a plurality of Sources simultaneously turned on to provide an electromagnetic beam which contains a broad frequency range. Especially, but not exclusively, in such a configuration it is beneficial to adjust said sources providing output in the range of 1.0 to 1.4 THz such that substantially the same results, (eg. ellipsometric PSI and/or DELTA), are achieved by analyzing output from any of the selected detectors in the frequency range of between about 1.0 to 1.4 THz. This not only provides continuity between the lower and upper extents of the frequency range, but provides an approach to assuring accuracy of results. If the same results are achieved using very different sources of electromagnetic radiation, both can be considered to very likely enabling acquisition of good data.

FIG. 1d is included to disclose that an Alternative Polarization State Generator (APSG) configuration involving an optional Polarizer (P) and a Modulator (MOD), can be applied. Such an (APSG) configuration can be employed instead of, or in addition to components in the Conventional Polarization State Generator (CPSG) shown in FIGS. 1a-1c. Also indicated is an Alternative Polarization State Detector Generator (APSD) configuration including a Modulator (MOD′). Again such an (APSD) configuration can be employed instead of, or in addition to the Conventional Polarization State Detector (CPSD) shown in FIGS. 1a-1c. It is noted that various types of Modulators exist, including those which apply an electric signal, or an acoustic signal or an optical signal to effect modulation of a polarization state.

Also shown in FIGS. 1a-1d is a Chopper (CH). This allows the beam to be “chopped” at a selected frequency so that it can be monitored separate from non-chopped background electromagnetic radiation. This enables obtaining data which is not overwhelmed by noise, in a non-darkened room. The Chopper (CH) is shown a being located differently in each of FIGS. 1a-1d. This is to indicate that there is no required position, with the only functional requirement being that the beam be chopped thereby. The system which comprises a Chopper (CH) will provide substantially only the chopped electromagnetic beam to the Detector (D1) (D2) D3).

FIG. 1e shows a system substantially similar to that in FIG. 1a, but note that the Odd Bounce Image Rotating System (OB) preceeds the Polarizer (P) in the Polarization State Generator (PSG). FIG. 1h also indicates that both the Odd Bounce Image Rotating System (OB) and Polarizer (P) are fitted with means, (eg. stepper motors), for effecting synchronized rotation of (MOB) and (MOP). In use a natural polarization state from the Source (S1) is azimuthally rotated by the Odd Bounce Image Rotating System (OB) and then passes through the Polarizer (P). In this system the Polarizer (P) is rotated azimuthally to correspond to the azimuthal position of the polarization in the electromagnetic beam as it exits the Odd Bounce Image Rotating System (OB). This approach has been found to work very well. The Odd Bounce Image Rotating System (OB) is substantially responsible for setting the azimuthal orientation of the beam polarization, and the Polarizer (P) “cleans-up” polarization of the beam exiting therefrom. FIGS. 1f and 1g are again very similar to FIGS. 1b and 1c, but with a similar reversal of position of the Odd Bounce Image Rotating System (OB) and the Polarizer, for the same purpose as indicated with respect to FIGS. 1e and 1a.

FIGS. 1i-1k show similar configurations to FIGS. 1e-1g, but note that a second Polarizer (P′) replaces the Odd Bounce Image Rotating Systems (OB) in FIGS. 1e-1g. In this case the second Polarizer (P′) serves to prevent Polarizer (P) being oriented so that it is at 90 degrees with respect to the natural polarization emerging from the Source (1) (S3) (S3), therefore blocking its transmission threthrough. By adding Polarizer (P′) it is possible to set Polarizer (P) at any azimuthal orientation and still achieve electromagnetic beam transmission therethrough.

FIGS. 1l-1o demonstrate various element configurations for a Terahertz ellipsometer or polarimeter.

FIGS. 1l and 1p show a Backward Wave Oscillator (BWO) is shown as Source for providing a partially linearly polarized Beam of electromagnetic radiation which is directed to pass through a focusing Lens (L), a Chopper (C), an Image Rotator (PR), a Polarizer (P) then interact with a Sample on a Stage (S), and then pass through a Rotating Analyzer (A) and enter a Golay Cell Detector (GC). More specifically FIG. 11p demonstrates an ellipsometer or polarimeter system sequentially comprising:

Said ellipsometer or polarimeter system can provide that said rotatable image rotation system (PR) is an odd bounce (OB) (OB′) optical image rotating system comprising an odd number of at least three (RE1) (RE2) (RW3) reflective elements, (see FIGS. 3a and 3b), oriented such that a beam of electromagnetic radiation provided by said source of electromagnetic radiation (BWO) interacts with each of said at least three reflective (RE1) (RE2) (RW3) elements of said at least one odd bounce optical image rotating system (PR) and exits therefrom along a non-deviated non-displaced trajectory, said beam of electromagnetic radiation also interacting with a sample system placed on said stage for supporting a sample system (S), and said analyzer (A) before entering said detector (GC). It is noted that the at least one odd bounce (OB) (OB′) optical image rotating system consists of a selection from the group consisting of:

FIG. 1p shows that said ellipsometer or polarimeter system which can further comprises at least one beam directing reflecting means (M1) (M2) (M3) (M4). Further, the sample supporting stage (S) can be part of a system (HG) for controlling the angle of incidence (Oa) at which a beam of electromagnetic radiation is caused to approach said sample.

Reference to FIGS. 1a-1o should be understood to show that the FIG. 1p system can comprise at least one rotatable or rotating polarizer, compensator and/or analyzer.

FIG. 1m is not to be confused with that in FIGS. 1l and 1p. Ithows a variation of the Rotating Analyzer THZ Ellipsometer system wherein the Image Rotating System is replaced with a second Polarizer (P2). In use relative rotation of Polarizers (P1) and (P2) adjusts the amount of polarized beam which exits (P2).

FIG. 1n shows a Rotating Polarizer THZ Ellipsometer system. Note that compared to FIG. 1l, FIG. 1n shows a Rotating Polarizer (RP) and a combination of Rotatable Analyzer (A) and Image Rotator (PR) after the Sanmple and Stage (S). The order of the Rotatable Analyzer (A) and Image Rotator (PR) can be reversed.

FIG. 1o shows a Rotating Compensator THZ Ellipsometer system. Note that both the Polarizer (P) and Analyzer (A) are rotatable, and an additional Rotating Compensator (RC) element, is present.

Turning now to FIGS. 2a-2d, insight to the operation of various Terahertz sources is provided. FIG. 2a shows that a Smith-Purcell (SP) cell comprises a Grating (G) and an electron beam (e) passing thereover, with the result being that THz electromagnetic radiation is emitted. FIG. 2b shows that a Free Electron Laser (FE) comprises a sequence of Magnetic Poles (MP), and again an electron beam (e) passing thereover, with the result being that THz electromagnetic radiation is emitted. FIG. 2c shows a Backward Wave Oscillator (BWO) comprises a Waveguide (WG) through which electromagnetic radiation (EM) is passed in one direction while an electron beam (e) passes therethrough in the opposite direction, again with the result that THz electromagnetic radiation is emitted. FIG. 2d demonstrates that a Terahertz source, (arbitrarily identified as (S1)), typically requires that a Frequency Multiplier (M) be present to provide an extended frequency range output, (eg. from 300 GHz or below through at least 1.4 THz). While not diagramatically shown, as there is really nothing to show, it is noted that an IR range Source of electromagnetic radiation is preferably a Fourier Transform Infrared (FTIR) Source which provides a spectroscopic range of wavelengths. It is noted that (FTIR) actually refers to an approach in analysis of a spectrum of wavelengths involving use of a means for collecting a multiplicity of wavelengths simultaneously, and application of a Fourier Transform to data, rather than via use of a monochromater. However, it is common to identify the Source of the spectrum of IR wavelenghts as an FTIR Source. It is specifically noted that while the Odd-Bounce Image Rotation System, (see FIGS. 3a and 3b), is present in the IR-VASE®, it has never been applied at frequencies below 10 THz. And specifically, it has not been applied in systems comprising a Backward Wave Oscillator (BWO) or a Smith-Purcell cell or a Free Electron Laser which provide frequencies down to 300 GHz or below. The application thereof at said frequencies is new with the described system. It is also new with the present invention to combine a FTIR Source with a Backward Wave Oscillator (BWO) or a Smith-Purcell cell or a Free Electron Laser to provide a practical system for practicing ellipsometry over a wide frequency range of from 300 GHz or below upward through the IR range.

FIGS. 2e and 2f demonstrate basic components of Detectors, (eg. Golay cell (GC) and Bolometer (BOL)). A Golay cell basically comprises two Chambers (CH1) and (CH2). In use electromagnetic radiation (EM) enters one Chamber (CH1) and heats a gas therein, which expands. This causes the Diaphram (DIA) to change shape which causes a Probe Beam (PB) entered to the Second Chamber (CH2) to reflect along a different pathway which is then detected by a detector (not shown). FIG. 2f shows that a Bolometer (BOL) operates by directing a electromagnetic radiation to impinge on a material (Ω) which changes resistance with its temperature. Also shown are a Voltage Source (V) and a Current Detector (I). In use a change in the current flow indicates that the electromagnetic radiation has heated the material (Ω). FIG. 2g show a demonstrative detector of Terahertz frequencies comprises a P/N junction onto which electromagnetic radiation (EM) is impinged, and which produces a measurable voltage (V). Further, while many materials can be applied in solid state devices, a particularly relevant material for application in THz and IR frequency ranges is disclosed as being “Deuterated Triglycine Sulfate”, which is typically referred to as (DTGS), optionally embedded in Poly-Vinylidene Fluroide (PVDF). Said material shows very high pyroelectric performance.

(Note, FIG. 2g should also be considered to present at least a portion of a solid state Source of Terahertz frequencies, wherein a voltage is applied, and electromagnetic radiation emission results. It is to be understood that Solid State Sources and Detectors for providing and detecting THz and/or IR frequency range electromagnetic radiation can be substituted for, or used in combination with any of the other types of Source and Detector types identified herein).

Turning now to FIGS. 3a and 3b, there is represented in FIG. 3a a three (3) bounce Odd Bounce image rotating system (OBIRS) comprising three (3) reflective elements (RE1), (RE2) and (RE3), oriented with respect to one another such that an input beam of electromagnetic radiation (EMI) exits as an output beam of electromagnetic radiation (EMO) without any deviation or displacement being entered into the locus thereof. FIG. 3b demonstrates a five (5) bounce odd bounce image rotating system (OBIRS) wherein five reflective elements (RE1′), (RE2′) (RE3′), (RE4′) and (RE5′) oriented with respect to one another such an input beam of electromagnetic radiation (EMI) exits as an output beam of electromagnetic radiation (EMO) without any deviation or displacement being entered into the locus thereof. Note generally that the angle of incidence of the (EMI) and (EMO) beams of electromagnetic radiation are nearer normal than is the case in the FIG. 3a three (3) bounce odd bounce image rotating system (OBIRS). This is beneficial in that the closer to normal the angle of incidence, the less aberration effects are entered to the beam. However, it is also to be appreciated that construction of the FIG. 3b system is more difficult than is construction of a FIG. 3a system.

FIG. 4 demonstrates a preferred compensator (C) (C′) for use in a rotating compensator ellipsometer system for application in the IR range of wavelengths. The compensator system comprises, as shown in upright side elevation, first (OS1) and second (OS2) orientation adjustable mirrored elements which each have reflective surfaces. Note the adjustability enabling pivot (PP1) (PP2) mountings. Said compensator system further comprises a third element (TE) which, as viewed in upright side elevation presents with first (IS1) and second (IS2) sides which project to the left and right and downward from an upper point (UP2), said third element (TE) being made of material which provides reflective interfaces on first and second sides inside thereof. Said third element (TE) is oriented with respect to the first (OS1) and second (OS2) orientation adjustable elements such that in use an input electromagnetic beam of radiation (LB) caused to approach one of said first (OS1) and second (OS2) orientation adjustable mirrored elements along an essentially horizontally oriented locus, is caused to externally reflect therefrom upwardly vertically oriented, (see beam (R1)) then enter said third element (TE) and essentially totally internally reflect from one of said first and second sides thereof, then proceed along an essentially horizontal locus (see beam (R2)), and essentially totally internally reflect from the other of said first (OS1) and second (OS2) sides and proceed along an essentially downward vertically oriented locus, (see beam (R3)), then reflect from the other of said first (OS1) and second (OS2) adjustable mirrored elements and proceed along an essentially horizontally oriented (LB′) propagation direction locus which is essentially undeviated and undisplaced from the essentially horizontally oriented locus of said input beam of electromagnetic radiation even when said compensator is caused to rotate about the locus of the beam of electromagnetic radiation, with the result being that retardation is entered between orthogonal components of said input electromagnetic beam of radiation. Also shown are third element lower side (IS3), with indication that it can be shaped as shown by (IS3′), and retain functionality.

FIGS. 5a and 5b demonstrate systems which can be used as Polarizer (P) and Analyzer (A) in FIGS. 1a-1c. FIG. 5a demonstrates a Polarizer (P) comprised of Non-Brewster Angle (NBR) and Non-Brewster (BR) Angle components. Shown is a beam of electromagnetic radiation (EMW) passing demonstrates a compensator design for optional compensators (C) (C′) will be present and caused to rotate during data acquisition and the odd bounce image rotating system (OBIRS) will be stepped to various azimuthal angle positions and set motionless during data acquisition, which the fixed linear polarizer (FP) and analyzer (A) (A′) are held stationary. That is, the preference is in a rotating compensator ellipsometer system, wherein the combination of the fixed polarizer and the odd bounce image rotating system (OBIRS) provide an effective rotatable polarizer. This is useful where a polarizer, (such as tipped wire grid plate polarizers used in the IR wavelength range), is difficult to rotate while maintaining alignment of the components therein and while avoiding deviation and displacement affects between input (EMI) and output (EMO) electromagnetic beams.

FIG. 5b demonstrates an alternative possible polarizer, comprising a dual tipped wire grid polarizer system comprising first (WG1) and second (WG2) wire grid polarizers which have fast axes of polarization oriented with their fast axes parallel to one another, each thereof having first and second essentially parallel surfaces. Note however, that the essentially parallel sides of (WG1) are tipped with respect to the essentially parallel sides of (WG2), as characterized by the angle (∝). The purpose of angle (∝) is to divert unwanted reflections (R1) and (R2).

Note that both Polarizers in FIGS. 5a and 5b provide substantially undeviated and undisplaced output beams therefrom, with respect to beams input thereto, even when the polarizer is rotated about the locus of a beam of electromagnetic radiation.

It is to be understood that while preferred embodiments of Polarizers provide a linear polarization as output, the described system can be used with a substantially linearly polarizing polarizer, or a polarizer which provides partially linearly polarization. In the Claims the term “polarizer” should then be interpreted broadly to mean preferably a linear polarizer, but including polarizers which provide partially linearly polarization. Further, in combination with a Compensator, other polarization states can be achieved.

FIG. 6 shows that a preferred embodiment of the system allows sample investigation in both the THz and IR ranges, (eg. from 300 GHz to abut 1.4 THz, and from about 1.0 THz and higher frequency). Further, it is indicated that below about 1.4 THz a first (S1) is used to provide the electromagnetic radiation, and above about 1.0 THz a second (S2) Source is used to provide the electromagnetic radiation. FIG. 6 shows an overlap in the range of about 1.0 to about 1.4 THZ, and that a described system preferably provides the same results, (eg. ellipsometic PSI and/or DELTA), when Detector output is analyzed to provide, for instance, a Sample characterizing PSI (Ψ), (or DELTA (Δ)). FIG. 6 should be viewed as demonstrating a concrete and tangible presentation of results which can be achieved by application of a described Invention.

FIG. 7 demonstrates displaying data (DIS) provided by a Detector (DET), (eg. D1, D2 D3 in FIGS. 1a-1d), obtained by practice of described systems using machine readable media of a computer (CMP), as well as indicates the Computer (CMP) can control Ellipsometer/Polarimeter elements operation.

Finally, it is specifically disclosed that a present invention system preferably comprises a Computer System which controls element motion, (eg. stepwise or continuous rotation of a Polarizer (P) and/or Compensator (C, C′) and/or Analyzer (A) and/or Odd Bounce Image Rotating System (OB); operation of a Chopper (CH); positioning of a Sample (S); selection of a Source (S1, S2); selection of a Detector (D1, D2, D3); and operation of a Source (S1, S2, S3) and/or Detector (D1, D2, D3). Further, a present invention system comprises a Computer System (CMP) which serves to analyze data provided by a Detector (D1, D2, D3) and Display said data or results of analysis thereof. That is, a present invention system can be considered to be a Computer System (CMP) which comprises an Ellipsometer or Polarimeter, which Computer System (CMP) controls operation of elements of said Ellipsometer or Polarimeter to the end that Sample characterizing Data is developed, as well as analysis of said data performed and presentation of said data, or results of analysis thereof.

Having hereby disclosed the subject matter of the present invention, it should be obvious that many modifications, substitutions, and variations of the present invention are possible in view of the teachings. It is therefore to be understood that the invention may be practiced other than as specifically described, and should be limited in its breadth and scope only by the Claims.

Herzinger, Craig M.

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